1. Field of the Invention
This invention relates to an air dryer device for drying compressed air of compressed air system, such as air brake, for a vehicle.
2. Prior Art
A typical example of conventional air dryer devices under consideration as disclosed in U.S. Pat. No. 3,464,186 comprises a housing having an open end, an end cover connected to the open end of the housing and having an inlet port and an outlet port, and a desiccant container mounted within the housing. Compressed air flows through the inlet port, the desiccant container and the outlet port. Part of the air passed through the desiccant container is frequently caused to backflow through the desiccant container to regenerate the desiccant therein, but when the drying ability of the desiccant becomes much lowered, the desiccant must be replaced by a new one. Upon studying the lowering of the drying ability of the desiccant, it has been found that it depends to a large extent upon an oil contamination rather than on a deterioration due to the lapse of time. This oil contamination arises from the fact that part of a lubricating oil for an air compressor is entrained in the compressed air and is introduced into the desiccant container. It has therefore been long desired to be able to easily check or inspect the degree of oil contamination so that the desiccant, when found contaminated beyond an acceptable level, can be replaced by a new one without delay.